Heat exchangers of the above type, especially of cross-counterflow construction, have been disclosed in EP-A-0331 026 and EP-A-0265 726. Heat exchangers of this type of crossflow construction are disclosed in US-A-3, 112, 793 where the tube matrix extends in a straight, undulating or diagonal arrangement between the respective main ducts or manifolds conveying the fluid to be temperature controlled. These heat exchangers can be used as exhaust gas heat exchangers or recuperators, where the tube matrix is arranged in the hot exhaust gas stream of a stationary or propulsion gas turbine engine and where a portion of the heat contained in the hot exhaust gas stream is used to heat compressed air for the combustion chamber in its passage through the tube matrix before reaching the combustion chamber.
Also discussed in DE-A-39 42 022, is the use of heat exchangers of crossflow or cross-counterflow construction as cooling air coolers (condensers) in hypersonic engines, where cooling air tapped at the intake end at a point upstream of the basic engine's compressor is liquified by, among other means, heat exchange with cryogenically fed fuel, such as hydrogen, and conveyed in its vaporous state to components requiring cooling.
In straight ramjet operation (hypersonic flight) the compressed ram air ducted to the ramjet engine through a variable air intake reaches temperatures of approximately 1500.degree. K and above, which exposes the tube matrix of the heat exchanger, when used as a cooling air cooler, to extremely high temperatures.
In all of the above-cited uses, the tube matrix and the necessary supports of the tubes of the matrix are subjected to correspondingly elevated temperatures. Perforated plates heretofore used as spacer supports are substantially unusable in this environment because they lack the required strength, rigidity, oxidation resistance and the like. The perforated plates also have the disadvantage of producing vibration-induced cracks at the perforations for the tubes which tend to render the plates unserviceable relatively early in their life. It has been proposed to provide spacer supports with metal felt strips, or wires or tapes to dampen the vibration, but these are comparatively unstable from a stress aspect and practically lack resistance to elevated temperatures, as do the perforated plates themselves. Apart from their comparatively complex construction, they also require additional external support such as, supporting frames, housings and the like as evident from EP-A-0389 759.